Methods and Systems for Testing a Fiber Optic Network

ABSTRACT

The present disclosure relates to a method for testing a fiber optic network including a fiber distribution hub. The method includes providing a test splitter within the fiber distribution hub to provide optical connectivity between an F1 fiber and at least a portion of an F2 fiber network. The method also includes testing sending a test signal from the F1 fiber through the test splitter to the F2 fiber network, and replacing the test splitter after testing has been completed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/047,486, filed Apr. 24, 2008, which applicationis hereby incorporated by reference in its entirety.

BACKGROUND

Fiber optic telecommunications technology is becoming more prevalent asservice providers strive to deliver higher bandwidth communicationcapabilities to customers/subscribers. The phrase “fiber to the x”(FTTX) generically refers to any network architecture that uses opticalfiber in place of copper within a local distribution area. Example FTTXnetworks include fiber-to-the-node (FTTN) networks, fiber-to-the-curb(FTTC) networks and fiber-to-the-premises (FTTP) networks.

FTTN and FTTC networks use fiber optic cables that are run from aservice provider's central office to a cabinet serving a neighborhood.Subscribers connect to the cabinet using traditional copper cabletechnology such as coaxial cable or twisted pair wiring. The differencebetween an FTTN network and an FTTC network relates to the area servedby the cabinet. Typically, FTTC networks typically have cabinets closerto the subscribers that serve a smaller subscriber area than thecabinets of FTTN networks.

In an FTTP network, fiber optic cables are run from a service provider'scentral office all the way to the subscriber's premises. Example FTTPnetworks include fiber-to-the-home (FTTH) networks andfiber-to-the-building (FTTB) networks. In an FTTB network, optical fiberis routed from the central office over an optical distribution networkto an optical network terminal (ONT) located in a building. The ONTtypically includes active components that convert the optical signalsinto electrical signals. The electrical signals are typically routedfrom the ONT to the subscriber's residence or office space usingtraditional copper cable technology. In an FTTH network, fiber opticcable is run from the service provider's central office to an ONTlocated at the subscriber's residence or office space. Once again, atthe ONT, optical signals are typically converted into an electricalsignal for use with the subscriber's devices. However, to the extentthat an end user may have devices that are compatible with opticalsignals, conversion of the optical signal to an electrical signal maynot be necessary.

FTTP networks include active optical networks and passive opticalnetworks. Active optical networks use electrically powered equipment(e.g., a switch, router, multiplexer or other equipment) to distributesignals and to provide signal buffering. Passive optical networks usepassive beam splitters instead of electrically powered equipment tosplit optical signals. In a passive optical network, ONT's are typicallyequipped with equipment (e.g., wave-division multiplexing andtime-division multiplexing equipment) that prevents incoming andoutgoing signals from colliding and that filters out signals intendedfor other subscribers.

A typical passive FTTP network includes fiber optic cables routed from acentral location (e.g., a service provider's central office) to a fiberdistribution hub (FDH) located in a local area such as a neighborhood.The fiber distribution hub typically includes a cabinet in which one ormore passive optical splitters are mounted. The splitters each arecapable of splitting a signal carried by a single fiber to a pluralityof fibers. The fibers split out at the splitter are routed from thefiber distribution hub into the local area using a fiber opticdistribution cable. Fibers are routed from the fiber distribution cableto subscriber locations (e.g., homes, businesses or buildings) usingvarious techniques. For example, fiber optic drop cables can be routeddirectly from a breakout location on the distribution cable to an ONT ata subscriber location. Alternatively, a stub cable can be routed from abreakout location of the distribution cable to a drop terminal. Dropcables can be run from the drop terminal to ONT's located at a pluralityof premises located near the drop terminal.

Once a fiber optic network has initially been installed, it is oftendesirable to test the performance of various fiber optic lines/circuitsin the network to make sure the lines/circuits satisfy certain minimumperformance requirements. Testing systems and methods that reduce laborand equipment cost are needed.

SUMMARY

Features of the present disclosure relate to methods and systems forefficiently testing fiber optic communications networks.

These and other features and advantages will be apparent from a readingof the following detailed description and a review of the associateddrawings. It is to be understood that both the forgoing generaldescription and the following detailed description are explanatory onlyand are not restrictive of the broad aspects of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a passive fiber optic network after initial deployment butprior to installation of drop cables;

FIG. 2 is a schematic depiction of a fiber optic tether having amulti-fiber connector connected to a loop-back plug;

FIG. 3 is a schematic depiction of a drop terminal having a loop-backarrangement; and

FIG. 4 is a schematic depiction of a system for testing a fiber opticcommunications network.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary passive optical network 100. As shown inFIG. 1, the network 100 is adapted to interconnect a central office 110to a number of end subscribers 115 (also called end users 115 herein).The central office 110 may additionally connect to a larger network suchas the Internet (not shown) and a public switched telephone network(PSTN). The various lines of the network can be aerial or housed withinunderground conduits (e.g., see conduit 105). A Network Operation Center(NOC) 111 is shown interfacing with the central office 110.

In general, the network 100 includes feeder distribution cables 120routed from the central office 110. The distribution cables ofteninclude a main cable or trunk, and a plurality of branch cables thatbranch from the main cable. The portion of network 100 that is closestto central office 110 is generally referred to as the F1 region. The F1portion of the network may include a feeder cable (i.e., an F1distribution cable) having on the order of 12 to 48 fibers; however,alternative implementations may include fewer or more fibers. Thenetwork 100 also has an F2 portion that includes cables and componentslocated in closer proximity to the subscriber/end users 115.

The network 100 also may include fiber distribution hubs (FDHs) 130 thatreceive branch fibers of the distribution cable 120 and that output oneor more F2 distribution cables 122. In general, an FDH 130 is anequipment enclosure that may include a plurality of optical splitters(e.g., 1-to-8 splitters, 1-to-16 splitters, or 1-to-32 splitters) forsplitting the incoming feeder fibers into a number (e.g., 216, 432,etc.) of output distribution fibers corresponding to the F2 distributioncables 122. The F2 distribution cables are routed from the FDH 130 tolocations in close proximity to the end users 115.

The network 100 typically includes a plurality of breakout locations 116at which branch cables (e.g., drop cables, stub cables, etc.) areseparated out from and optically coupled to trunks of the distributioncables 122. Breakout locations 116 also can be referred to as taplocations or branch locations and branch cables also can be referred toas breakout cables or tethers. At a breakout location, fibers of thetrunk of the distribution cable can be broken out and connectorized toform a connectorized tether. In other embodiments, fibers of the trunkcan be broken out and spliced to a length of optical fiber having aconnectorized free end so as to form a connectorized tether.

Stub cables are typically branch cables that are routed from breakoutlocations 116 to intermediate access locations, such as a pedestals,drop terminals 104 or hubs. Intermediate access locations can provideconnector interfaces located between breakout locations 116 and thesubscriber locations 115. A drop cable is a cable that typically formsthe last leg to a subscriber location 115. For example, drop cables canbe routed from intermediate access locations to subscriber locations115. Drop cables also can be routed directly from breakout locations 116to subscriber locations 115, thereby bypassing any intermediate accesslocations. FIG. 1 shows the network after installation of thedistribution cables and drop terminals, but before installation of dropcables. Upon completion of the network, drop cables will typically beinstalled to form the final legs between the subscribers 115 and theintermediate locations (e.g., drop terminals 104) or between thesubscribers 115 and the break out locations 116.

In certain embodiments, factory integrated terminations may be used atthe F1 and/or the F2 region to provide environmentally sound and costeffective splicing protection. Factory integrated terminations refer tothe use of factory integrated access (tap) points at specifiedlocations, such as at breakout locations 116, in the network 100 insteadof field installed splices. These access points 116 may be connectorizedto provide a simple plug and play approach in the distribution portionof the network 100 when connecting subscribers 115 to the network 100.For example, implementations consistent with the principles of thedisclosure may include tethers terminated by rugged outside plantconnectors that can include single or multi-port connectors. Examples ofconnectors and/or receptacles that may be adapted for use on the distalend of a tether are further described in U.S. Pat. No. 7,264,402 andU.S. Patent Application Ser. No. 61/029,524, that are herebyincorporated by reference in their entireties.

In certain embodiments, loop back devices/arrangements can be used tofacilitate testing the transmission capabilities of the network. FIG. 2illustrates a loop back plug 300 for use in testing the network ofFIG. 1. The distribution cable F2 of the network of FIG. 1 includes atrunk cable and a plurality of tethers 340 that branch from the trunkcable at factory installed breakout locations. At least some of thetethers 340 are pre-connectorized with connectors 358. Each of theconnectors is adapted to interconnect with a corresponding loop backplug 300 to facilitate testing of the network. The loop back plug 300may be configured to couple a first fiber in the tether 340 to a secondfiber in the tether 340. For example, the loop back plug 300 is shownoptically coupling fiber 301 a of the tether to fiber 301 b of thetether. The loop back plug 300 also couples fiber 301 c of the tether tofiber 301 d of the tether. The loop back plug 300 can include amulti-termination (MT) ferrule 307 defining multiple fiber openings orbores receiving fibers that define fiber loops 309. The bores of theferrule 307 align with corresponding bores defined in a ferrule 359 ofthe connector 358 such that the ends of the fiber loops 309 align withthe ends of the fibers 301 a-301 d. When the connectorized tether 340 isready to be brought into service, the loop back plug 300 can be removedfrom the connector 358 and a connector corresponding to a branch cablesuch as a drop cable or stub cable can be plugged into the connector358. While 4 fibers are shown in the arrangement of FIG. 2, it will beappreciated that any number of fibers may be used. For example, incertain embodiments, systems having tethers, connectors and loop backplugs suitable for accommodating 12 fibers can be used. FIG. 3 showsanother loop back arrangement suitable for facilitating testing of thenetwork of FIG. 1. The loop back arrangement is shown used incombination with a drop terminal 104. The drop terminal 104 includes ahousing 401 that receives an end of a stub cable 402 containing fourfibers 403 a-403 d. The fibers 403 a-403 d are each optically connectedto an interior fiber optic connector located within the housing 401. Forexample, the interior fiber optic connectors can be mounted directly onthe fibers 403 a-403 d, or can be mounted at the ends of pigtails thatare spliced to the optical fibers 403 a-403 d. The interior fiber opticconnecters are plugged into inner ports of fiber optic adapters 405a-405 d that are mounted to an exterior wall of the housing 401. Thefiber optic adapters 405 a-405 d include outer ports that are accessiblefrom outside the housing 401. Loop back connector arrangements 409optically interconnect fiber optic adapters 405 a to fiber optic adapter405 b; and also optically connect fiber optic adapter 405 c to fiberoptic adapter 405 d. In this way, the loop back connector arrangements409 provide optical links/paths that optically connect optical fiber 403a to optical fiber 403 b and also optically connect optical fiber 403 cto optical fiber 403 d. The loop back connector arrangements 409 includeoptical connectors inserted in the outer ports of the adapters 405 a-405d and linking fibers that extend between ports 405 a and 405 b andbetween ports 405 c and 405 d. When the drop terminal 104 is ready to bebrought into service, the loop back assembly 409 can be removed from theports of the adapters 405 a-405 b and connectors corresponding to dropcables can be inserted into the ports. While 4 ports have been shown onthe drop terminal 104, it will be appreciated that any number of portsmay be used. For example, in one embodiment, drop terminals having 12ports for accommodating stub cables having 12 fibers can be used.Further details regarding drop terminals can be found at U.S. patentapplication Ser. Nos. 11/728,043 and 60/978,638, that are herebyincorporated by reference in their entireties.

A typical FDH includes a cabinet enclosing one or more splitters forsplitting signals transmitted to the FDH from an F1 distribution cable.Common splitters used in an FDH include 1×8 splitters, 1×16 splittersand 1×32 splitters. The splitters are each typically housed within amodule housing that is mounted within the cabinet of the FDH. An opticalfiber from the F1 distribution is optically connected to a splitterwithin the FDH to provide an input signal to the splitter. The splittersplits the input signal into a plurality of outputs. The outputstypically include fiber optic pigtails having connectorized ends thatcan be plugged into a first side of a termination field 500 (see FIG. 4)including a plurality of fiber optic adapters 501. Connectors opticallyconnected to fibers of an F2 distribution cable are plugged into asecond side of the termination field 500 such that the fiber opticadapters 501 optically connect the outputs from the splitter to theoptical fibers of the F2 distribution cable. Further details regardingfiber distribution hubs are provided at U.S. patent application Ser. No.11/544,951 that is hereby incorporated by reference in its entirety.

Referring to FIGS. 1 and 4, to test fibers that are routed to apre-connectorized tether with a loop back plug, a test signal can betransmitted from the Network Operation Center 111 to the central office110. From the central office 110, the signal travels through a F1distribution cable 120 to the FDH 130. Within the FDH, the signaltravels through the splitter 510 and the termination field 500 of theFDH 130 to the F2 distribution cable 122. The F2 distribution cable 122carries the signal to one of the preconnectorized tethers 340 equippedwith one of the loop back plugs 300. At the loop back plug 300, thesignal is looped back to another fiber of the tether 340 therebyallowing the signal to travel in a reverse direction back through thetether 340 to the main trunk of the F2 distribution cable 122. The maintrunk of the F2 distribution cable 122 carries the signal back to theFDH 130. Within the FDH 130, the signal travels back through thetermination field 500 and the splitter 510 to the F1 distribution cable120. The F1 distribution cable 120 carries the signal back to thecentral office 110. From the central office 110, the signal istransmitted back to the Network Operation Center 111. Properties of thereturn signal detected at the NOC 111 provide an indication of thefunctionality of the optical fibers of the distribution cable beingtested.

Referring still to FIGS. 1 and 4, to test fibers that are routed to adrop terminal with a loop back arrangement, a test signal can betransmitted from the Network Operation Center 111 to the central office110. From the central office 110, the signal travels through the F1distribution cable 120 to the FDH 130. Within the FDH, the signaltravels through the splitter 510 and the termination field 500 to the F2distribution cable 122. The F2 distribution cable carries the signal toa stub cable that carries the signal to one of the drop terminals 104with one of the loop back arrangements 409. At the loop back arrangement409, the signal is looped back to another fiber of the stub cablethereby allowing the signal to travel in a reverse direction backthrough the stub cable to the main trunk of the F2 distribution cable.The main trunk of the F2 distribution cable 122 carries the signal backto the FDH 130. Within the FDH 130, the signal travels back through thetermination field 500 and the splitter 510 to the F1 distribution cable120. The F1 distribution cable 120 carries the signal back to thecentral office 110. From the central office 110, the signal istransmitted back to the Network Operation Center 111. Properties of thereturn signal detected at the NOC provide an indication of thefunctionality of the optical fibers of the distribution cable beingtested.

Use of loop back devices may eliminate shuttling back and forth betweendifferent locations of the network when testing is performed.Eliminating shuttling can produce significant time and cost savings whentesting deployed distribution cables. An exemplary methods of testing afiber drop terminal or connectorized tether from a single location areshown in U.S. patent application Ser. Nos. 11/198,848 and 11/406,825,the disclosures of which are hereby incorporated by reference.

Within the FDH, the splitter/splitters provide optical links between theF1 distribution cable and the F2 distribution cable. The optical linksprovided by the splitters allow signals to pass through the FDH therebyallowing test equipment at the NOC to “see through” the FDH to test theF2 distribution cable network. However, when a network is deployed, itis common to install the full F2 distribution cable network, but to onlyoptically connect a portion of the full F2 network to an F1 distributioncable through the FDH. For example, when the F1 distribution cable isinitially installed, only a limited number of subscribers are typicallyavailable to receive service. Therefore, to defer cost, the FDH is notfully loaded with enough splitters to provide service to all of theoptical lines/ports of the full F2 network. Instead, only enoughsplitters are provided to serve the needs of the existing subscribersplus a limited additional capacity. As subscribers become available,splitters are added to the FDH to add capacity to match the demand. Inthe meantime, the portion of the F2 distribution network that is notcoupled to a splitter can not be tested from the central office or theNOC. To test these lines, it is necessary to send a technician to theFDH.

To overcome the above problem, instead of using one or more standard1×32 splitters during initial deployment of a network, a custom testsplitter or splitters can be used that provide optical connectionsbetween an F1 distribution cable and all the deployed fibers of an F2distribution network served by to the FDH. In this way, all of the F2network served by the FDH could be tested remotely from the NOC of theCO. Example custom test splitters could include splitter modules thatprovide a splitter ratio greater than 1×32, or greater than or equal to1×64, or greater than or equal to 1×128, or greater than or equal to1×256. Other example splitter ratios include 1×144, 1×288 and 1×432.Such splitters would likely introduce higher loss due to the high splitratios, but each splitter could also be lower cost per port/line sinceit would be integrated into one module. Additionally, in certainembodiments, the return loss of the various ports of the splitter couldbe “tuned” so that each one had a unique signature detectable at theNOC. For example, each port on the splitter could have a slightly higherloss so that an Optical Time Domain Reflectometer (OTDR) at the NOCcould detect easily the different ports. For instance, port 1 may beassigned a 17 dB of loss, port 2 may be assigned a 17.5 dB of loss, port3 may be assigned a 18 dB of loss, and so on for each of the ports.

In practice, the custom splitter manufacturer/supplier could provide aservice provider with one or more custom splitters and factory testedtuned/unique return loss data for each of the ports of the splitters.The custom test splitter could be sold to the service provider incombination with an FDH (e.g., the custom test splitter could bepre-loaded in the FDH by the manufacturer/supplier). When the serviceprovider initially installs the FDH in the field, the one or more customsplitters can be used to provide optical connectivity through the FDH toall of the outgoing F2 fibers intended to be served by the FDH. When theinstallation is complete, the custom splitter/splitters along with thedata regarding the factory tested loss for each of the splitter portscan be used by the service provider to remotely test the entire F2distribution network intended to be served by the FDH. After testing,the custom splitter/splitters can be removed and replaced with standardsplitters that provide enough capacity to serve the subscriber demand atthe time. Typically, to defer cost, the FDH would not be fully loadedwith splitters at that time. The custom test splitter/splitters removedfrom the FDH could be sent back to the manufacturer/supplier for credittoward future or current purchases. The manufacturer/supplier couldretest the custom test splitter/splitters to ensure they could be usedagain. If the custom test splitter/splitters performed at an acceptablelevel, the custom test splitter/splitters could be sold with anotherFDH.

From the forgoing detailed description, it will be evident thatmodifications and variations can be made without departing from thespirit and scope of the disclosure.

1. A method for testing a fiber optic network including a fiberdistribution hub, the method comprising: providing a test splitterwithin the fiber distribution hub to provide optical connectivitybetween an F1 fiber and at least a portion of an F2 fiber network;testing sending a test signal from the F1 fiber through the testsplitter to the F2 fiber network; and replacing the test splitter aftertesting has been completed.
 2. The method of claim 1, wherein theportion of the F2 fiber network includes a distribution cable having apre-connectorized tether connected to a loop-back device capable oflooping back the test signal.
 3. The method of claim 1, wherein theportion of the F2 fiber network includes a distribution cable havingconnected to a drop terminal at which a loop-back device for loopingback the test signal is located.
 4. The method of claim 1, wherein thetest splitter has a split ratio greater than 1×32.
 5. The method ofclaim 1, wherein the test splitter has a split ratio greater than orequal to 1×64.
 6. The method of claim 1, wherein the test splitter has asplit ratio greater than or equal to 1×128.
 7. The method of claim 1,wherein the test splitter has a split ratio greater than or equal to1×256.
 8. The method of claim 1, wherein the test splitter has a splitratio of 1×144.
 9. The method of claim 1, wherein the test splitter hasa split ratio of 1×288.
 10. The method of claim 1, wherein the testsplitter has a split ratio of 1×432.
 11. The method of claim 1, whereinthe test splitter includes splitter output lines each having a uniquedetectable signature.
 12. The method of claim 1, wherein the testsplitter includes splitter output lines each having a different returnloss.
 13. The method of claim 1, wherein the test splitter includes oneor more test splitters, and wherein the one or more test splitters allowthe entire F2 fiber network serviced by the fiber distribution hub to betested at the time the fiber distribution hub is initially installed.